Test Procedures - Loads
Compressor
Failure to start.
All have resistance start, capacitor run type motors.
Check voltage to compressor at the contactor.
Compare the idle voltage (compressor off) to the
active voltage (compressor starting). The supply
voltage must not be less than the lowest rated
voltage for the ice machine. If the voltage is
correct, proceed to the next step.
Check starting components. All models use a
PTCR to cut power to the start winding after the
compressor has started. Check the PTCR for
resistance. The resistance check must be when the
PTCR is at room temperature – any temperature
between 50 and 100.
At that temperature resistance should be very low
between 25 and 50 ohms. Also check resistance to
ground, it should be infinite. If the PTCR is good,
check the compressor windings.
Measure resistance from Common to ground. It
should be infinite. Measure resistance from
Common to Run – compare to the chart. Measure
resistance from Common to Start – compare to the
chart.
Compressor check for high amp draw. Measure
amp draw of starting circuit. If it does not drop off
immediately after start up, the PTCR should be
replaced. It is not practical to check a PTCR for
resistance at high temperatures as the resistance
drops very fast as the PTCR’s temperature falls. If
the compressor is drawing excessive amps but is
operating, the run capacitor may be open.
Disconnect electrical power, discharge the
capacitor and measure its resistance. If open,
replace it. If shorted to ground, replace it.
Any time the compressor is replaced, the PTCR
and run capacitor should also be replaced, or if the
model was equipped with a potential relay, start
capacitor and run capacitor, those should be
replaced with the compressor. Most Scotsman
service compressors include those parts.
Fan motor
1. Test using the controller’s indicator lights.
Note: Fan pressure control connection must be
jumped to perform this test.
Put the controller into test mode (depress Off for 3
seconds then depress Clean for 3 seconds). At the
end of the test cycle, the fan motor will be powered
and the Condenser Fan motor indicator light will be
on. The fan motor should start and run at that time.
If it does not, repeat the test but check the voltage
to the fan motor, it must receive full voltage at the
fan motor lead connection at the end of the test. If
there is voltage and the motor does not operate,
replace the motor. If there is no voltage, check the
controller high voltage harness connection. The fan
motor lead is the top wire. Check voltage from it to
ground, at the end of the test, when the fan motor
indicator light is On, there must be voltage from this
pin to ground. Note: high voltage power is supplied
to the bottom pin from the contactor line. Refer to
the machine wiring diagram as needed.
2. Test using an ohmmeter.
Disconnect electrical power.
Unplug fan motor from harness. Measure fan motor
winding resistance. If open, replace the fan motor.
May 2008
Page 37
CU1526, CU2026, CU3030
Service Manual
Electrical Shock
Hazard
.
Use extreme caution
while performing
diagnostic
procedures.
Electrical Shock
Hazard
.
Disconnect electrical
power before
beginning diagnostic
procedure.
